But others choose to believe. And, as journalist Jesse Walker reveals in his well-received new book, many of the scoffers – some of them card-carrying members of the educated elite – are susceptible to certain kinds of conspiracy theories.

I asked Walker, an editor at the libertarian Reason magazine and author of The United States of Paranoia: A Conspiracy Theory, to explore our tradition of finding sinister plots where none exist.

(That's right, they're all bogus. Every last one of them. Or at least that's what those of us who are in on it would like you to think.)

Q: What do we need to have in place for a conspiracy theory to develop?

A: Conspiracy theories emerge where three things collide.

The first is our natural tendency to find patterns and create narratives, to try to turn all these stray signals we receive into some sort of coherent order.

Second is a situation that we're suspicious of and makes us fearful.

And third is the fact that there are actual cases of people conspiring. There's a reason why there's a legal offense called conspiracy. It's not like being afraid of some supernatural monster that people talk about but never shows up.

Q: You write about conspiracy theories that popped up around the time of the American Revolution. What were they about?

A: Pamphlets that were distributed among the founding fathers were filled with conspiracy theories about the British: Not only are they enacting these various policies that limit our liberty and self-government, but there's also a conspiracy to destroy our liberty.

There are echoes in texts such as the Declaration of Independence, which is not just a list of things that King George III has been doing but also presents them as part of a design to bring the colonists "under absolute despotism."

It shows how there can be good reasons behind a conspiracy theory even when it's inaccurate. The British weren't twirling their mustaches and deciding how to rush the colonists and enslave them. But they weren't sitting there with no intent, either.

Q: Conspiracy theories are sometimes actually true, correct?

I talk about the post-Watergate investigations that exposed bona fide misbehavior by the CIA and the FBI. They not only showed that conspiracies were real but lowered the bar for imagining far-out conspiracies.

Q: When conspiracies get mentioned, some people accuse the believers of being mentally ill. Is that a real issue among conspiracy believers?

A: When a story catches on with enough people, we're not talking about mental illness. If believing in conspiracy theories is a sign of mental illness, it means 90 percent of Americans have been crazy since the beginning.

We're talking about folklore. Even if it says nothing that's true, it says something true about the anxieties and experiences of those who believe and repeat the theory.

Q: Can a conspiracy theory help someone avoid responsibility for their own actions?

It's certainly true that political figures, whether earnestly or opportunistically, can blame their problems on hidden forces as a way of sidestepping what they've done wrong.

Nixon is a classic example. He was filled with personal paranoia, some of which had to do with of genuine things that happened in the rough-and-tumble world of politics. But he used them as a way to justify unconscionable behavior.

Q: Why should readers bother to understand the tradition of conspiracy theories in America?

A: Conspiracies are a really good way to explore the history of the country through what people have been afraid of. You get this panoramic view of American fears and, to some extent, American hopes.